PLC control system and electrical control system distinguish the

PLC control system compared with the electrical control system, there are many similarities, there are many different. The difference is mainly in the following areas:
1) Judging from the control method, the electrical control system control logic hardware wiring, mechanical relay contacts using series or parallel, etc. combined into a control logic connections are many and complex, bulky, power consumption, system configuration, the I would like to change or add functionality more difficult. In addition, a limited number of contacts of the relay, the electrical control system flexibility and scalability is very limited. The PLC technology uses a computer, which controls the way the program logic is stored in memory, to change the control logic simply by changing the program, which is easy to change or increase the system functionality. System wiring small, small size, low power consumption, and PLC-called "soft-relay" is essentially a state of the memory cells, so "soft relay," the number of contacts is unlimited flexibility and scalability plc controller manufacturer system good .
2) From the work point of view, in the relay control circuit, when the power is turned on, the circuit is subject to all relays are in the state, that is, the pull of the relays are energized at the same time, should not be subject to some kind of pull-in relay conditions can not pull, this way of working called parallel work. The plc ethernet module user program is executed cyclically according to a certain order, so that each soft relays are in a cyclical scan cycle turned in by the same conditionality order each relay operation depends on the program scan order, this way of working is called Serial work.
3) Judging from the speed control, relay control system relies on mechanical contact action to achieve control, low operating frequency, mechanical contacts will appear jitter. The PLC to achieve control of program instructions by controlling the semiconductor circuit, high speed, program instruction execution time in microseconds level, and will not appear contact bounce problem.
4) Judging from the timing and the counting control, electrical control system uses the operating time of the relay delay the time control, time delay relay susceptible to ambient temperature and temperature changes, the timing accuracy is not high. The PLC semiconductor integrated circuit as a timer, a clock pulse is generated by a crystal oscillator, high precision, wide time range, the user can set the timer value in the program as needed to facilitate changes, affected by the environment, and the PLC have counted functions, and electrical control systems generally do not have the counting function.
5) From the point of view of reliability and maintainability, since the electrical control system uses a large number of mechanical contact which mechanical wear, arc burns, short-lived, multi-link system, the reliability and maintainability of the more difference. The PLC large number of switching operation performed by non-contact semiconductor circuit to complete its long life, high reliability, PLC also has a self-diagnostic function, able to detect its own fault, displayed to the operator at any time, and can dynamically monitor control the implementation of the program for on-site commissioning and maintenance more convenient.